1. Field of the Invention
The present invention relates to an illumination apparatus, particularly relates to an illumination apparatus adopted light emitting diodes as light sources.
2. Description of Related Art
Light emitting diodes have advantages of saving electrical power, which makes them possible to replace traditional light bulb and to be used as next generation light sources.
White light emitting devices, which are most popularly used in the field of general lighting, need to be packaged before they are applied into practical use. They usually have some packaging processes described hereinafter. At first, a light emitting chip is disposed on a substrate, and a florescent layer for converting light wavelength is formed on the light emitting chip. Then, liquid encapsulating material is further formed on the florescent layer and the light emitting chip. Then, a curing treatment is performed to cure the liquid encapsulating material so as to seal the fluorescent layer and the light emitting chip. Besides, a lens with specific curvature can be formed on the encapsulating material to control the divergent angle of the light emitted from the light emitting chip.
Conventional fluorescent layer is made by dispensing or coating a liquid layer on the top face and peripheral face of the light emitting chip and then curing the liquid layer. However, the surface of the liquid fluorescent layer is affected by the surface tension and is usually of spherical shaped. Therefore, consistent thickness is hard to obtain on both the top face and peripheral face of the light emitting chip. Consequently, white light emitted from the light emitting diodes can not be uniform in all directions.
In another aspect, since each individual packaged light emitting device can only provide a small amount of light intensity, a plurality of packaged light emitting devices have to be arranged together on a circuit board to get enough light intensity for practical use. For aesthetic purpose, an additional transparent cover is provided on the circuit board to cover the circuit traces and the electronic elements on the circuit board. However, transparent cover will partially absorb or reflect the light emitted from the packaged light emitting devices. That leads to decreasing the amount of light available for use. Besides, the transparent cover also increases the manufacturing cost.